no-non-null-assertion
Disallow non-null assertions using the
!
postfix operator.
Extending "plugin:@typescript-eslint/recommended"
in an ESLint configuration enables this rule.
Some problems reported by this rule are manually fixable by editor suggestions.
TypeScript's !
non-null assertion operator asserts to the type system that an expression is non-nullable, as in not null
or undefined
.
Using assertions to tell the type system new information is often a sign that code is not fully type-safe.
It's generally better to structure program logic so that TypeScript understands when values may be nullable.
module.exports = {
"rules": {
"@typescript-eslint/no-non-null-assertion": "warn"
}
};
Examples
- ❌ Incorrect
- ✅ Correct
interface Example {
property?: string;
}
declare const example: Example;
const includesBaz = foo.property!.includes('baz');
interface Example {
property?: string;
}
declare const example: Example;
const includesBaz = foo.property?.includes('baz') ?? false;
Options
This rule is not configurable.
When Not To Use It
If your project does not use the strictNullChecks
compiler option, this rule is likely useless to you.
If your code is often wildly incorrect with respect to strict null-checking, your code may not yet be ready for this rule.